상용 핵설계 적용을 위한 2단계 봉단위 노심 계산 체계 개발

학위논문(박사) -- 서울대학교대학원 : 공과대학 에너지시스템공학부, 2021.8. 이지은.A pin-wise three-dimensional nuclear design code newly has been developed as an effort to establish more accurate, yet practically applicable to commercial nuclear designs. As neutronics solvers, the numerical methods based on the traditional diffusion theory are implemented with the pin-wise finite difference method (FDM) and coarse mesh finite difference (CMFD) method coupled with the semi-analytic nodal method and evaluated which numerical method is practically desired. The planar parallelization method and the two-level CMFD acceleration method are incorporated to achieve high calculating performance. Since the lattice calculation based on MOC is still used to generate pin-wise group constants for each slice of an assembly, the pin-wise equivalence factors such as the flux discontinuity factors or the super homogenization factors are examined to preserve the higher order solutions of the lattice calculation. The accuracy and performance of the proposed methods are tested with the C5G7MOX, VERA, BanDi-50 and APR1400 benchmark problems. The results indicate the superiority of the pin-wise calculations compared to the traditional node-wise calculations and the computing time and resources are reasonable for the commercial reactor core designs. To assess transient calculation capability, SPERT III E-Core transient problems are solved. With the proper kinetic nuclear parameters, the pin-wise transient calculation shows good agreement on the higher order solutions.1. Introduction 1 2. Calculational Method 5 2.1. Two-step core calculation procedure 5 2.2. Pin-wise homogenization 6 2.3. Volume Adjustment 10 2.4. Pin-wise equivalence factors 13 2.5. 3D pin-wise calculation with 2D/1D decoupling method 20 2.6. Two-level CMFD acceleration 24 2.7. Transient Calculation 29 3. Assessment 33 3.1. Discontinuity Factor vs SPH Factor 33 3.2. L336C5 3D Benchmark Problem 40 3.3. VERA Benchmark Problem 44 3.4. Small Modular Reactor (BanDi-50) Calculation 50 3.5. APR1400 Benchmark Problem 60 3.5.1 Overview of the APR1400 PWR initial core 62 3.5.2 Generation of the Pin-wise Homogeneous Cross-sections 70 3.5.3 Numerical Results 75 3.5.4 Calculation Performance 108 3.6. SPERT III E-Core Transient Calculation 110 3.6.1 Modelling for nTRACER calculation 111 3.6.2 Generation of the pin-wise cross-section 118 3.6.3 Numerical results 121 4. Conclusions 128 5. References 131박